The invention relates to cyclodextrin glycosides and processes for their preparation.
Cyclodextrins, also called cycloamyloses, cyclo-malto-oligosaccharides or Schardinger dextrins, are cyclic (1.fwdarw.4) .alpha.-linked glucopyranoses. They are prepared by enzymatic degradation of starch. Cyclohexa-, cyclohepta-, and cycloocta-amylose, also called .alpha.-, B, .gamma.-cyclodextrin, are mainly formed by this process.
In addition to these cyclodextrins, branched cyclodextrins are also known. These are also called cyclodextrin glycosides of G.sub.n -cycloamyloses, n indicating the number of .alpha.-D-glucopyranosyl groups in the side chains. They are thus cyclodextrins in which at least one hydroxyl group is linked to glucose, maltose, maltotriose or also generally to substituted or unsubstituted malto-oligosaccharides. Only cyclodextrin glycosides containing unsubstituted malto-oligosaccharides can be prepared to date.
The branched cyclodextrins are chiefly prepared by the action of enzymes on a mixture of the cyclodextrins and maltose or maltotriose, such as is described for example, in the paper "Some Properties and the Inclusion Behavior of Branched Cyclodextrins" by Y. Okada, Y., Kubota, K. Kiozumi, S. Hizukuri, T. Ohfuji and K. Ogata in Chem. Pharm. Bull. 36 (6), 2176-2185 (1988).
A preparation of di-O-.alpha.-maltosyl-B-cyclodextrin ((G.sub.2).sub.2 -B-cyclodextrin) from maltosyl fluoride and cyclodextrins with subsequent enzymatic degradation to give di-0-glucosyl derivatives is to be found in the paper "Structure of Di-0-.alpha.-Maltosyl Cyclodextrins produced from .alpha.-Maltosylfluoride and Cyclodextrins" by Y. Yoshimura et al. in Agric. Biol. Chem. 54 (10), 2585-2591 (1990).
It is also known that the mother liquors of industrial B-cyclodextrin preparations also contain small amounts of branched cyclodextrins (K. Koizumi et al., Carbohydr. Res. 201, 125-134 (1990)).
All of the processes described so far have the common features of the use of enzymes for the preparation of the branched cyclodextrins and an expensive isolation of amounts in the mg to g scale.
The pyrolysis of B-cyclodextrin in a temperature range from 135.degree. C. to 220.degree. C. leading to branched cyclodextrins is moreover the subject matter of U.S. Pat. No. 4,904,307. Pyrolysis of a mixture of glucose and cyclodextrins at a temperature of 160.degree. C. in the presence of catalytic amounts of a fumaric acid gives similar results (T. Okemoto, K. Hara, H. Ishigami, K. Mikuni, T. Oosawa, Jpn. Kokai JP 89,138,202 (1989)).
The high reaction temperature during the preparation of the branched cyclodextrins is a disadvantage in both cases. It leads to unwanted by-products and makes working up and purification of the reaction products is difficult.
All the branched cyclodextrins prepared by the processes mentioned so far are cyclodextrin glycosides in which the cyclodextrin is linked with glucose or oligomers of glucose, such as, for example, maltose or malto-oligosaccharides.